mp_msg: don't change text color for normal output

Normal text was set to gray foreground color. This didn't work for
terminals with white background.

Instead of setting a color for normal text, reset the color attributes.
This way, only errors and warnings are formatted differently.

Also change the default color for MSGL_HINT from bold white to yellow.
input: make input command deprecation warnings visible

Some time ago, all old special-cased commands (like "volume 1" to change
volume by one) have been removed. These commands are still emulated
using simple text replacement. This emulation is done to not break
everyone's input.conf, especially because the input.conf provided by
standard mplayer* still uses the old commands.

Every use of a deprecated command prints a replacement warning, which
was visible only with -v. Make these warnings visible by default.

There's actually not much reason to do this, but since commands like
"volume 5 1" don't work anymore, it's better to be verbose about this.

Also simplify the replacement for "vo_fullscreen".
command: export VO video width/height as properties

Add new properties "dwidth" and "dheight", which contain the video
size as known by the VO (not necessarily what the VO makes out of them,
i.e. without window scaling and panscan).
mplayer: cosmetics: make some code more readable
mplayer: make --frames=1 work for audio

This has the same (useless) definition as frame stepping in audio-only
mode: one frame means one playloop iteration. (It's relatively useless,
because one playloop iteration has a random duration. But it makes
--frames=1 work, which is useful again.)
core: output --playing-msg message only after at least one frame is shown

This way it's possible to retrieve correct information about video, like
actual width/height, which in general are available only after at least
one frame has been sent to the video output, such as dwidth/dheight.

mpv_identify.sh becomes a bit slower, because we let it decode enough
audio and video to fill the audio buffers and to send one frame to the
video output. Also, --playing-msg isn't shown anymore with --frames=0
(could be fixed by special-casing it, should this break any use cases).

Note that in some corner cases, like when the demuxer for some reason
returns lots of audio packets but no video packets at the start, but
video actually starts later, the --playing-msg will still be output
before video starts.
mpv_identify: allow specifying mpv binary via MPV

Useful for testing.
mpv_identify: add --quiet to mpv command line

Prevents the status line from being printed. Otherwise, the status line
is always printed due to --frames=1, and it's visible on the terminal
because it's printed to stderr.
m_option: pretty-print floats with 3 pre-decimal digits instead of 2

There were complaints that ${fps} was printed as e.g. "23.98" instead of
"23.976". Since there's no way to format floats exactly _and_ in a user-
friendly way, just change the default precision for printing floats.